The expression of endogenous type C RNA-viral genes in mammalian tissues under the influence of hormones are being investigated. Current studies include: 1) the identification of the level, i.e., transcriptional of translational, which estrogen hormones control in the expression of viral genes in the NIH/Swiss mouse uterus by nucleic acid hybridization; 2) the expression of viral genes during embryological development; 3) the association between endocrine changes induced in the pituitary-adrenal axis by oophorectomy and oncornaviral genes in the etiology of adrenal carcinoma in mice.